1. Field of the Invention
The present invention relates to a method for measuring the recirculation rates in an internal combustion engine so as to monitor the recirculation device with which said engine is equipped.
2. Description of the Prior Art
Existing known methods for measuring the flow of exhaust gas consist in using a diaphragm having a known section and measuring upstream and downstream pressures, and then calculating flow. Such methods are relatively imprecise since if this device is directly applied to the recirculation system of the engine, it is necessary to correct the calculated values, both in terms of pulse rate and gas density (temperature-composition) to obtain a flow-weight ratio.
Installation of such a device is not always easy and furthermore causes a disturbance of the recirculation device's operation due to load losses. In addition, if one wishes to know the rate of recirculation, it is necessary to measure the flow of gas taken in by the engine, and this is complicated.
Means for directly determining the flow of recirculated gas and, at the same time, the rate of recirculation, can therefore not be presently effected in a simple way on an engine. In the after-sale period, it is therefore particularly difficult to ensure proper functioning of a recirculation device installed on the engine. The sole approximative method consists of removing the recirculation device and testing it on a stand devised for this purpose. The test stand must be equipped with two depressurization sources, one of which serves to control the device while the other is intended to create a flow of air in the apparatus being measured, where it is at least possible to measure one section of passage.
This second method of operation entails the following disadvantages: it is necessary to remove the device from the engine to test it on the stand, then to replace it once the test is over; the conditions in which the device is tested are different from operating conditions (temperature, vibrations, etc.), which may prevent a flaw in the functioning of the device under real conditions from showing up; it is difficult to obtain test conditions with control pressures and flow which approximate reality.